The presence of thrombus, or blood clot, within arteries, veins, grafts, and vascular channels of the bodies is a challenge to many disciplines of medicine. If the thrombus develops acutely, it may create a medical emergency. Even if the thrombus develops gradually, conservative medical management with drugs is frequently less than satisfactory. Surgical intervention is an alternative, although a costly, and, at times, an ineffective one in many cases. Catheter directed thrombolysis is effective, but time consuming and very costly, because of the expense of the drug and the intensive care needed to monitor this therapy. A successful catheter infusion thrombolysis may take 36 to 48 hours to achieve complete thrombolysis.
Mechanical thrombolytic devices have been developed which are quick and effective in dialysis grafts, mainly because of the nature of such fresh unorganized clots presented in such situations, but such devices are not effective in removing most of the thrombus in arteries and veins of the body. Many of these mechanical devices have the potential to damage the endothelium of the arteries and veins, as well. The endothelium is a fragile covering of the inside of arteries and vessels, and is easily damaged with mechanical forces. This may cause a cascade of events resulting in thrombosis, restenosis, accelerated atherosclerosis, valvular dysfunction, platelet aggregation, late thrombus formation, and other untoward events. By damaging the endothelium during percutaneous thrombolysis, long term patency of the vessel is compromised.
Many mechanical thrombolytic devices have been developed to hasten the process of non-surgically eliminating clot from blood vessels, but in most cases, they fail to remove all of the clot. This necessitates an additional procedure of protracted infusion of a thrombolytic drug, which is the procedure the mechanical thrombolytic devices were designed to replace.
Mechanical devices exist that also deliver a drug to aid in the dissolution of thrombus, but are utilized and then removed, usually in 20-40 minutes. Such methods and devices do provide mechanical action over a protracted period of time while the drug is being infused. As a result, there is invariably thrombus remaining at the termination of the procedure, necessitating the infusion of a thrombolytic drug through a different catheter for a protracted period of time to eliminate the remaining clot. This proves costly as more resources in the form of personnel and the expensive drugs are consumed.
The prior art mechanical thrombolytic devices and the prior art combination mechanical-pharmacologic devices are therefore designed to be operated mechanically for short periods of time, usually 20-40 minutes total, and at very high speeds or frequencies. Prior art devices are designed to act in short, intense bursts and involve rotating baskets and brushes, propellers, water jet, Venturi effect, vibrational, and other mechanical methods. The mechanical action is often effective in debulking, or lessening, the clot burden, but rarely effective in removing or dissolving all of the clot. Part of the reason is that a clot adherent to the wall of the vessel is not affected by these mechanical devices. The use of these devices to perform the incomplete mechanical thrombolysis necessitates a procedure which demands the attention and the time of a physician, a nurse, and several technologists in an interventional suite, catheterization lab, or operating room.
The prior art devices are also expensive, typically costing $500-700 or more. This tremendous expenditure of time, effort, and supplies is usually not rewarded with complete success, creating a need to place another expensive infusion catheter within the clot, transferring the patient to an intensive observation area, and infusing thrombolytic drug(s) for a protracted period. The patient is then returned to the interventional suite many hours later, and most often, the action of the thrombolytic drug has resulted in complete thrombolysis with no residual clot.
The net consequence is that a lot of time, energy, personnel, and money are expended with the use of prior art mechanical and pharmaco-mechanical devices, with incomplete results, necessitating the use of a relatively long infusion to effect complete thrombolysis. Therefore, the use of the prior art devices to dissolve a clot during the course of a procedural intervention is unsatisfactory, and an unnecessary consumption of resources. Moreover, the design and speeds at which such devices operate risk significant injury to a patient.
The existing mechanical and pharmacomechanical devices also suffer from a design that limits the thrombolytic action to an area near the tip of the catheter. This is true of the rotating baskets, propeller type devices, rotating brushes, water jet, ultrasonic, sub-sonic, vortex, and other mechanical thrombolytic devices. Many of these can be activated for only short periods of time, i.e., seconds or minutes, lest they overheat or cause hemolysis or blood loss. There is a real potential for many of them to damage the endothelium, or lining of the blood vessels, if used for more than a few seconds at a time. Moreover, the pharmacomechanical devices have apertures for injecting the thrombolytic drug near the tip of the catheter as well. While these designs may be satisfactory for a short segment occlusion of 10 cm. or so, frequently the occlusion because of thrombus is much longer. Such prior art devices must be advanced and retracted within the lumen of the occluded vessel to “treat” one segment of the vessel at a time, usually resulting in incomplete and ineffective treatment of the entire occluded segment, thus requiring the need for the patient to undergo a prolonged infusion of the thrombolytic drug with the attendant increase in costs. Typically, the thrombus within the deep venous system of the leg needing interventional therapy extends from the calf veins to the inferior vena cava, a length of 40-60 cm. Femoral-popliteal arterial grafts are 30 cm. or so.
There are many prior art devices for the treatment of thrombus or blood clot within the arteries and veins of the body, as the occurrence of blood clots is a common and serious medical condition. The trend toward lesser invasive procedures has benefited patients in improved outcomes, less morbidity, and without the need for surgery. There are many prior art catheters designed for infusion of lytic agents, such as urokinase and tissue plasminogen activator substance (tPA). Representative of these are U.S. Pat. Nos. 4,968,306, 5,250,034, 5,267,979, 5,624,396, 5,782,797, and 5,425,723. The process of infusion and dissolution of the thrombus is a lengthy one, taking 24 to 48 hours frequently. The lytic agent bathes the thrombus and pharmacologically dissolves the thrombus over time. Such methods necessitate the use of a large amount of expensive drug or lytic agent and overnight monitoring in a critical care unit. The process may cost upwards of $20-30,000.
Purely mechanical thrombolytic devices were developed as an alternative to infusion thrombolysis. These devices attempt to dissolve the clot in a relative short procedure, usually less than an hour. Representative of these are U.S. Pat. Nos. 4,747,406, 4,923,462, 5,569,275, 5,397,293, 5,766,191, and 5,997,558. While they may be effective in removing a large amount of the thrombus in a relatively short period of time, there is usually incomplete thrombus removal necessitating further infusion of lytic agents to dissolve the residual thrombus. Moreover, they remove enough of the clot so that partial flow may be reestablished within the vessel, causing the lytic agent to be washed out of the clot containing vessel as it is being infused.
Combination devices which utilize mechanical thrombus disruption and pharmacological agent infusion are represented by U.S. Pat. Nos. 5,279,546, 5,197,946, 5,362,309, 5,279,456, 5,725,494, and 5,713,848. These combination devices are an improvement, in that they attempt to utilize a lytic agent and mechanical motion of various types to disrupt the clot. They however, are time inefficient and the action of the lytic agent usually takes hours to achieve complete thrombolysis. All of the prior art combination devices are used within the confines of a procedural intervention that takes less than an hour and would damage the endothelium if used for more protracted periods of time. Many would overheat or fail, as the mechanical motion demands high frequency vibrations or rotation. Even Dubrul, U.S. Pat. No. 5,731,3848 at the lowest frequency of one vibration/second, would damage the endothelium if activated for several hours.
There is a dichotomy in the design of all of these prior art thrombolytic catheters. The pure infusion catheters only passively bathe the clot and have no method of increasing the surface area of the clot to be dissolved. They demand very protracted infusions to clear the clot. The purely mechanical devices diminish clot burden, at a cost of time, materials, and personnel, but frequently leave significant residual clot requiring a prolonged infusion. The combination pharmaco-mechanical devices attempt to fragment the clot and deliver the lytic agent simultaneously, but are only able to be mechanically active for short periods of time, usually not enough time for the lytic agent to dissolve the clot.
Therefore, there is a need for a device which provides a mechanical action to increase the surface area of the clot for efficacious dissolution by the lytic agent, provides this mechanical action for a prolonged period of time while the lytic agent is acting, provides a mechanical action which is not harmful to the endothelium of the vessel, and is time efficient for the operator and the patient.